The goal of this research is to facilitate efforts to understand brain function. The immediate goal is the construction of a neural cell culture system that recapitulates with one of the brain's principal memory circuits - the trisynaptic pathway of hippocampus: entorhinal cortex (EC), dentate gyrus (DG), CA3 and CA1 regions. The brain on a chip technology employed combines precisely controlled cell culture, state-of-the-art cell culture media, large scale microelectrode arrays, newly developed directional microtunnels for guiding neural growth with near patch-clamp quality recording of axon potentials, and advanced algorithms for detecting patterns of activity distributed across many neurons and electrodes. Specific hypotheses will be tested as to the computations performed by the different tissues, how they their responses change with stimulation, and how network level feedback influences how information is represented. The research is highly innovative and highly risky. The potential payoff is substantial, as the paradigm being created and investigated provides a basis for others to investigate many hypotheses as to normal and abnormal brain circuit function in a distributed fashion, whereas current practice is for single neuron or average activity. The potential exists for the creation of a new and more powerful technology for the routine screening of new drugs for their effects on memory. The specific aims are: Aim #1: Develop the technology for culturing dissociated neural networks of two distinct anatomical regions with connections comprising axons extending unidirectionally through guiding microtunnels. Develop protocols for stimulation, recording and analysis. Test that dissociated tissues maintain their salient in vivo properties. At the end of Aim 1, we will have established functional capability (stimulation, characterization), and also will understand differences in the representation of information in each hippocampal subregion Aim #2: Test the principal computational and learning properties of two components: DG and CA3. At the end of Aim 2, we will have established circuit responses distinct and appropriate to the two tissue types and exploited their likely very different connectivity and response patterns to induce plastic change. Aim #3: Evaluate CA1 as a correlator and novelty discriminator in the completed EC-DG-CA3-CA1 circuit, including feedback to the entorhinal cortex. Learn how feedback reinforces circuit responses. Aim #4: Test the hypothesis that a very effective means of inducing repeatable patterns of activity is through stimulation at theta frequencies (4-10Hz) with phasic encoding. Completion of these aims will provide a novel engineered platform for basic and applied science. It will increase our understanding of the advantages of staged signal processing in information analysis.